U.S. Pat. No. 3,751,303 to Kittl discloses an energy conversion system which includes a rare earth oxide selective emitter and a photovoltaic cell to provide thermal-to-photo-to electrical energy conversion. Likewise, U.S. Pat. No. 3,929,510 to Kittl discloses a solar radiation conversion system which includes a solar radiation-to-silicon cell spectral matching means having ytterbium oxide applied as a layer or coating.
U.S. Pat. No. 4,776,895 to Goldstein discloses a thermophotoceramic doped with a rare earth metal oxide. The photovoltaic selector is matched to the emitter so as to absorb radiation in the same bands as the emitter.
U.S. Pat. No. 4,707,560 to Hottel et al is directed to a thermophotovoltaic system including a rare earth emitter disposed concentrically within a photocell array matched to the frequency of the emitter.
U.S. Pat. No. 4,750,943 to Nelson describes a thermophotovoltaic system including a narrow band emitter spaced and optically isolated from the thermal energy source of the system. A photocell array is optically coupled to the emitter.
U.S. Pat. No. 4,746,370 to Woolf is concerned with a photothermophotovoltaic converter which is used to convert solar radiation to heat. The heat is used to excite an emitter which radiates onto a photovoltaic panel.